1. Field of the Invention
The present invention relates to an agricultural spray adjuvant for use with herbicides. More particularly, the invention relates to the use of tetrapotassium pyrophosphate as the spray adjuvant in herbicidal compositions to increase the absorption and overall efficacy of post-emergence herbicides.
2. Description of the Prior Art
Herbicidal compositions in the form of dusts or liquids frequently include a surface-active agent of the kind referred to in the art as wetting, dispersing, or emulsifying agents. These agents permit the compositions to be readily dispersed in water to provide aqueous solutions for convenient spray applications. The surface-active agents employed for this purpose can be of the anionic, cationic, or nonionic type and include, for example, ethylene oxide condensation products with alkyl phenols or long-chain alcohols such as polyoxyethylated octyl phenol or stearyl alcohol, polyethylene oxides, the alkali metal or amine salts of an unsaturated fatty acid such as sodium oleate and dimethylamine oleate, the sulfonated animal and vegetable oils such as sulfonated fish and caster oils, sulfonated petroleum oils, sulfonated acyclic hydrocarbons, sodium salts of sulfonated condensation products of naphthalene and formaldehyde, the alkaline earth salts or amine salts of alkylbenzenesulfonates, sodium alkyl aryl sulfonates, partially esterified polyhydric alcohols such as diglycol monostearate, soluble sulfates such as sodium lauryl sulfate, quaternary ammonium compounds such as alkyl dimethylbenzyl ammonium chloride and the like. For further examples of other suitable surface-active dispersing agents, reference is made to U.S. Pat. No. 3,852,058 to Huffman and the publication "Detergents and Emulsifiers Annual" by John W. McCutcheon Inc., Morristown, N.J.
While herbicidal compositions containing the aforementioned agents generally promote a more even distribution of the herbicide when applied as foliar sprays, certain limitations of each type of spray additive have been recognized in the art. One such problem associated with the use of these spray adjuvants in herbicidal compositions has been the inability of the target plant tissue to absorb effective amounts of the herbicide based on a single application. The proposed remedy to this problem has been to increase the application dosage in an attempt to facilitate the desired absorption. However, this results in the inefficient use of the herbicide which can prove to be uneconomical and wasteful of materials. Also, the use of excessive quantities of certain herbicides can cause undue foliage "burn" or plasmolysis due to the retention of the herbicide on the leaf surface for prolonged periods of time. Besides this deleterious effect to target plant leaves, which may be considered as merely cosmetic, relatively high levels of certain herbicide and adjuvant residues lingering on non-target agronomic species to which they may be applied can result in increased crop damage and can even poison the soil permanently.
Another limitation associated with the use of conventional spray adjuvants in herbicidal compositions has been that of temperature restrictions during the application season. For example, as temperatures rise to 85.degree. and above, spraying operations have to be suspended in many instances to avoid leaf burn due to poor uptake of the herbicide by plants at such elevated temperatures. Moreover, it should be noted that most spray additives are preferably used in conjunction with post-emergence herbicides and the usual time for many of these post-emergence applications is in late spring and summer. This is the time when day temperatures reach levels that cause both target and non-target plant species to be more likely stressed and, therefore, less receptive to foliar uptake of non-nutrient materials. Further, application of herbicides during periods when spray ceiling temperatures are lowered often compounds the problem of controlling weeds because other conditions such as increased field moisture and humidity, which generally accompany lower temperatures, contribute to the growth of existing weeds, as well as the germination and subsequent emergence of greater numbers of weed and grass species. In addition, post-emergence herbicides are generally ineffective when applied at temperatures below 70.degree.-75 .degree. F. or at very high temperatures, 95.degree. F. and higher, because the possible pathways into the plants are substantially cut off under these conditions, making absorption of the herbicide extremely difficult.
Since the effectiveness of a given herbicide largely depends on its ability to enter the stomata of target plants, the development of herbicidal spray additives in the art has necessarily focused on those selective additives which have experimentally demonstrated their capacity to increase the overall uptake of a particular herbicide. However, there is a need in the art for an improved herbicidal spray adjuvant which addresses the environmental conditions under which the herbicidal compositions are conveniently applied, as well as the physiological characteristics of target and non-target plant species themselves.